N-14 QUADRUPOLE COUPLING-CONSTANTS AND N-14 AND F-19 SPIN ROTATION COUPLING-CONSTANTS OF NITROSYL FLUORIDE, FNO, AND NITRYL FLUORIDE, FNO2

High-resolution pure rotational spectra of nitrosyl fluoride, FNO, and nitryl fluoride, FNO2, have been measured using a cavity pulsed microwave Fourier-transform spectrometer. The samples were prepared using a pulsed electric discharge through precursor substances, with the discharge apparatus mounted as part of the pulsed nozzle of the spectrometer. Nuclear quadrupole and magnetic hyperfine structures due to N-14 and F-19 have been resolved for both molecules, and precise values for the nuclear quadrupole and spin-rotation coupling constants have been obtained. The N-14 quadrupole coupling constants of FNO2 have been rationalized in terms of a sigma-withdrawal of electron density from NO2 towards F. This view is corroborated by the magnetic shielding estimated from the F spin-rotation constants.